This invention relates to control of a toroidal continuously variable transmission.
Tokkai 2000-18373 published by the Japanese Patent Office in 2000 discloses a feedback control device of a toroidal continuously variable transmission (hereafter, referred to as TCVT).
This control device controls a real speed ratio to a target speed ratio using a mechanical feedback device which feeds back the displacement of a power roller to an oil pressure system that causes the power roller to displace, and a feedback controller which performs proportional/integral/differential (PID) control of the oil pressure system based on the difference between the real speed ratio and the target speed ratio.
The speed ratio of the TCVT varies according to the gyration angle of the power roller, but this relation is not linear. Thus, this control device expresses a relation between the displacement of the power roller and the speed ratio as a second differential derivative, and calculates a transfer function from the target speed ratio to the real speed ratio by the second differential derivative. By suitably setting various constants in the transfer function, stability of response of speed ratio control is obtained and overshoot is prevented.
In this control device, in calculating the transfer function from the second differential derivative, a differential of a time-variant factor representing the relation between the displacement and the gyration angular velocity of the power roller, and a differential of a first order partial differential derivative that represents the relation between the gyration angle and controlled variables, are both considered to be zero.
However, it is not correct to consider these time differentials to be zero from the viewpoint of speed change response in the speed change transient stage. For example, if it is considered that a time differential is zero when the target speed ratio varies from a small speed ratio to a large speed ratio, in the early stages of the speed ratio variation of the TCVT, the speed change response will exceed the linear characteristic defined by the transfer function, and in the latter half of the speed change variation, the speed change response is less than the linear characteristic defined by the transfer function. When the target speed ratio varies from a large speed ratio to a small speed ratio, the reverse phenomenon occurs. This error is more evident, the larger the speed change rate.
It is therefore an object of this invention to reduce the error between the speed change response of the toroidal continuously variable transmission, and the target linear characteristic.
In order to achieve the above object, this invention provides a control device of a toroidal continuously variable transmission for a vehicle. The vehicle comprises an accelerator pedal. The toroidal continuously variable transmission comprises an input disk, an output disk, a power roller which transmits torque between the input disk and the output disk, and a trunnion which supports the power roller free to rotate. The trunnion comprises a trunnion shaft and the power roller varies a gyration angle (xcfx86) according to a displacement (y) of the trunnion in the direction of the trunnion shaft to vary a speed ratio of the input disk and output disk. The transmission further comprises an oil pressure actuator which drives the trunnion in the direction of the trunnion shaft.
The control device comprises a control valve which supplies oil pressure to the oil pressure actuator, a mechanical feedback mechanism connecting the trunnion and the control valve to feed back the displacement of the trunnion to the control valve, a valve actuator which controls the control valve according to a command value (u), a sensor which detects a rotation speed (xcfx89co) of the output disk, a sensor which detects a depression amount (APS) of the accelerator pedal, a sensor which detects the gyration angle (xcfx86) of the power roller, a sensor which detects the displacement (y) of the trunnion in the direction of the trunnion shaft, and a programmable controller.
The controller is programmed to calculate a target control variable (z*) which is a target value of a control variable (z) being an object of control, based on the accelerator pedal depression amount (APS) and the output disk rotation speed (xcfx89co), calculate a time-variant coefficient (f) representing the relation between the displacement (y) of the trunnion in the direction of the trunnion shaft and a variation rate ({dot over (xcfx86)}) of the gyration angle (xcfx86) of the power roller, calculate a first time differential ({dot over (f)}) which is a time differential of the time-variant coefficient (f), and determine the command value (u) by applying a control gain based on the first time differential ({dot over (f)}).
This invention also provides a control method of a toroidal continuously variable transmission for a vehicle. The vehicle comprises an accelerator pedal. The toroidal continuously variable transmission comprises an input disk, an output disk, a power roller which transmits torque between the input disk and the output disk, and a trunnion which supports the power roller free to rotate. The trunnion comprises a trunnion shaft and the power roller varies a gyration angle (xcfx86) according to a displacement (y) of the trunnion in the direction of the trunnion shaft to vary a speed ratio of the input disk and output disk. The transmission further comprises an oil pressure actuator which drives the trunnion in the direction of the trunnion shaft, a control valve which supplies oil pressure to the oil pressure actuator, a mechanical feedback mechanism connecting the trunnion and the control valve to feed back the displacement of the trunnion to the control valve, and a valve actuator which controls the control valve according to a command value (u).
The control method comprises detecting a rotation speed (xcfx89co) of the output disk, detecting a depression amount (APS) of the accelerator pedal, detecting the gyration angle (xcfx86) of the power roller, detecting the displacement (y) of the trunnion in the direction of the trunnion shaft, calculating a target control variable (z*) which is a target value of a control variable (z) being an object of control, based on the accelerator pedal depression amount (APS) and the output disk rotation speed (xcfx89co), calculating a time-variant coefficient (f) representing the relation between the displacement (y) of the trunnion in the direction of the trunnion shaft and a variation rate ({dot over (xcfx86)}) of the gyration angle (xcfx86) of the power roller, calculating a first time differential ({dot over (f)}) which is a time differential of the time-variant coefficient (f), and determining the command value (u) by applying a control gain based on the first time differential ({dot over (f)}).
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.